1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, in which data based on image data are stored in a memory, and a recording medium having a program recorded thereon.
2. Description of Related Art
Recently, there has been widely used an image forming apparatus, such as a network type of copier, printer, MFP (multifunction peripherals), etc. which receives print data, namely, image data in a form of PDL (Page Description Language), produced by an external device, e.g., a PC (Personal Computer), through a network, e.g., a LAN, converts the received print data temporarily into data in an intermediate form (intermediate data) to store in a memory, reads the stored intermediate data sequentially to convert into bitmap data, and then prints out. The PDL typically includes PostScript (TM) and PCL (Printer Control Language).
There is a demand for higher throughput in such an image forming apparatus for an increase of print data according as printing process speed has become higher. The apparatus has to hold print data until the printing has been completed, because when a certain error occurs, printing has to be resumed from the page where the error occurred. Further, when a memory has not an enough empty area, the memory cannot store new data and a memory-over error resultantly occurs. Accordingly, memory capacity needs to be increased for processing large data simultaneously and higher cost results, which leads to a problem.
In order to avoid such an increase of memory capacity, there has been applied processing of compression or the like to data to be stored for decreasing the memory capacity, but such a method needs additional processing for compressing process, which causes the throughput to be reduced.
There has been also adopted a method to improve efficiency for using a memory by managing intermediate data and bitmap data in a common memory with use of a threshold value. However, with this method, data is just held according to a simple compared result of determination as to whether the empty area of the memory is larger than the threshold value, and processing stops until the memory secures an empty area larger than the threshold value. This also leads to a problem of reducing the throughput.
Further, JP 2000-165634A discloses an apparatus that stores image data in a memory, the apparatus including a check means for checking whether the memory has an enough capacity of empty area to store the image data, and a data compression means that, when the check result by the check means is negative, selects data possible to delete or compress out of the data stored already in the memory and either deletes or compresses the selected data.
However, in the above-described technique, when the memory is short of empty areas, the apparatus determines existence of bitmap data in the midst of printing process, deletes the data after completion of the output in case that the data exists, and compresses the data possible to be compressed (intermediate data converted to bitmap data) to produce an empty area in case that the bitmap data does not exist. Therefore, a chance to produce the empty area by deleting the data is substantially limited to the time after completion of printing process. In case that the data does not exist, data compression processing is executed, which causes a problem of necessitating process time. As a result, the apparatus needs time for securing an empty area in the memory and has difficulty in achieving high throughput.